Differential operated overspeed motor control



Feb. 9, 1960 A- H. MYLES DIFFERENTIAL OPERATED OVERSPEED MOTOR'CONTROLFiled June 18, 1958 2 Sheets-Sheet 1 10 \2.? II POWER vAR\AE L.E mSOURCE SPEED LOAD MOTOK 22 DIFFERENTIAL MOTOR DIRECTION I r n CONTROL.5W\TCH J I7 I 8 9? IZI MOTOR INVENTOR.

A5A H. MYLES Feb. 9, 1960 MYLES ,767

DIFFERENTIAL OPERATED OVERSPEED MOTOR CONTROL Filed June 18, 1958 2Sheets-Sheet 2 E555 lNCKq- ISCEI INCEZ USRI INVENTOR. 2 ASA H. MYLE5,

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United States PatentO DIFFERENTIAL OPERATED OVERSPEED MOTOR CONTROL AsaH. Myles, Solon, Ohio, assignor to Square D-Company, Detroit, Mich., acorporation of Michigan Application June 18,1958, Serial No. 742,867

1 Claim. (Cl. 318-323) This invention is directed to a control mechanismfor controlling the energization and de-energization of a motor, andmore particularly for disconnecting a motor from its source of power oreffectively de-energizing the motorswhen the speed of the motor reachesa certain predetermined speed. It is understod that the term disconnectis used herein in its electrical sense to include the opening of thecontacts as well as the operating of other motor control devices, suchas static switches, to terminate power transmission from a power sourceto the motor, thereby de-energizing the motor. I

In the past, devices have been devised which disconnect at least one oftwo hoist motors from the power lines if respective parts of the hoistreach a predetermined positional relationship. An example of such deviceis illustrated in a patent, No. 2,328,697, issured to Paul White onSeptember 7, 1943, for Limit Switch and Control System Combination, andassigned to the commonassignee of the present application. It isparticularly noted that the, aforementioned patent is directed to thecontrolling of the motors in response to the relative position ofcertain parts of the hoisting apparatus, for example, to prevent jammingthe crane hook in the boom, and not solely to therelative speeds of themotors.

In many installations of electric motors, either A.C. or DC. it isdesirable to have a motor connected to and energized by its source ofpower so long as the motor is running within a desired speed rangeextending between one speed and a predetermined certain speed. In

these installations it is also desirable to de-energize the motor or todisconnect the motor from its source of power when the speed of themotor reaches that certain speed to prevent the motor continuingoperation at a speed out- I side of the desired speed range.

The certain speed may be either at the lower speed end or at the higherspeed end of the desired speed range, depending upon the particularapplication and use of the variable speed motor. I

In the past, various devices and apparatus have been used in the controlof and protection of motor and which effect a deenergization of themotor or a disconnection of v by the average workmen in industry. In thepast rugged speed control deviceshave not been as accurate as desired,and highly perfected, intricate, and more exact devices have not beenable to withstand the rugged applicationsto which they are subjected.

. It is well recognized that controls for a DC. hoist motor have, up tothe present time, been less expensive and more safe than controls forAC. hoist motors. At the same time DC. motors were more costly to buildand operate than A.C.' hoist motors. Hoists drivenby A. Q.

2,924,767 Patented Feb. 9, 1960 safety purposes when polyphasealternating current motors of the induction type are used since thecontrol must preventoverspeeding of the motor, vparticularly in the caseof overhauling loads. If the hoist motor is permitted to overspeed, thedanger of dropping a load, or not being able to stop a load at the endof its travel is increased to the point where it is possible to damagethe hoist or other structures. At the same time it is desired to operatethe motor at speeds up to its maximum safe speed and withoutdisconnecting the motor until its speed has reached that certainpredetermined safe maximum speed.

Another application wherein the present control may be used is for motordriven grinding wheel or, the like, wherein it is desired to shut downor stop the grinding wheel if the speed thereof reaches a certainminimum speed.

One of the objects of the present invention is to overcome theaforementioned problems and others.

A further object of the present invention is to provide rugged anddurable structure which will operate with a high degree of accuracy todisconnect a motor from its source of power when the speed of the motorreaches a certain speed.

A still further object of the invention is to provide speed responsivestructure which will disconnect a mine hoist motor from its source ofpower if overspeeding of the motor starts to take place.

Another object of the invention is to provide a control mechanismcomprising a differential having first and .second members adapted to bedriven at the same speed differential element and the control means toeffect operation of the control means in response to the differential inspeeds of the members.

Further objects and a better understanding of the invention wil becomeapparent from the following description and the attached claim taken inconjunction with the accompanying drawings, in which:

4 Fig. 1 illustrates the features of the invention in block diagram typedrawings, and

Fig. 2 illustrates a control incorporating an embodiment of theinvention for use in a mine hoist.

An embodiment of the invention is illustrated in Fig. 1 for thepurpose'of exemplification and not of limitation. In this embodiment avariable speed motor 10 is energized by a power source 11 for driving aload 12. The motor 10 is connected and disconnected from the powersource 11 and is controlled by a motor control 13 which is interposedbetween the motor 10 and the power source/11.

The motor control 13 is connected to the power source "switch 18 and amotor 19 which is operable at a con! stant "speed. The motor 19 may be aconstant speed motor, or a variable speed motor controlled to operatecontinuously at a constant speed. The differential used herein has inputmembers 20 and 21 and a ditferential element 22 dri-vingly couplingmembers 20 and 21. Element 22=is' movable relative to input members 20and 21, and, in the present example, is revolvable about the axis of themembers '20 and 21. In such a differential the speed of rotationand thedirection of rotation of the element;22 is dependent on the relativespeeds of and directions of rotation of the members 20 and 21.

In this instance the member 20 is connected by suitable mechanicalconnection, represented by the dash-dot line 23, to the mechanicalconnection 16 of the variable speed motor 10. Similarly, the member 21is mechanically connected, as represented by the dash-dot line 24, tothe motor 19. 'It is understood that the mechanical driving connectionsrepresented by the dash-dot lines 23 and 24 may be a direct drivewherein the members 20 and 21- rotate at the same speed as the speeds ofthe respective motors and 19 or that the driving connections may includespeed changing devices so that the input members 20' and 21 rotate at apredetermined ratio to the speeds of their respective motors.

Best results have been obtained by rotating members 20 and 21 inopposite directions relative to each other and when the differentialoperates in a manner wherein element 22 revolves about the axis ofmembers 20 and '21 in one direction when member 20 is rotating slowerthan member 21, element 22 stands still when the members 20 and 21 arerotating at the same speed, and element 22 revolves in the oppositedirection when the mem ber 20 rotates faster than the member 21. Thisfeature is used to carry out the present invention by mechanicallyconnecting the direction switch 18 to the element 22 by a suitablemechanical connection, represented by the dashdot line 25, andconnecting the direction switch through suitable electrical connections,represented by solid line 26, in or to the motor control 13.

The direction switch 18 is of standard construction such that movementof element 22 in one direction holds the switch 18 in one position andmovement of the element 22 in the opposite direction moves the switch toits opposite position. In one of these positions the switch Thedirection'switch 18 and the motor control 13 may I be interconnected sothat'the variable speed motor 10 will be disconnected from power source11 upon the speed of the motor 10 reaching a certain maximum speed atthe nect, at least one of the motors, and preferably at least thevariable speed motor 10 from the source of power 11. The certain speedof the variable speed motor at which the direction switch 18 is operatedis very accurately established since the element 22 stops to change itsdirection of rotation at that speed. Since the direction of rotation ofthe element 22 is very accurately dependent on the relative. speeds ofthe members 20 and 21, the operation of or movement of switch 18 fromits position permitting energization of variable speed motor 10 to itsposition causing deenergization of the variable speed motor isaccurately and positively effected.

Fig. 2 illustrates the embodiment of the invention of Fig. 1 as appliedto a mine hoist wherein it is desired to disconnect a variable speedhoist motor upon its speed reaching a maximum safe speed at the upperend of a desired speed range. In this particular application loads, suchas a skip N and a skip S are to be alternately raised and loweredfrom amine, skip N being raised while skip S is being lowered and vice versa.Each skip. is. suspended 'byits respective cable N and S from itsrespective drum source 111. The motor control 113 is connected to thepower source by suitable wires including wires 114L 114L and l14L and isconnected to the motor 110 by suitable wires including wires 115L and115L and Each motor 110 is connected to the drums DN and DS throughsuitable mechanical linkage or mechanical driving connections,represented by the dash-dot line 116 in the drawing. The system alsoincludes a dilferential 117, a directional switch 118 and a constantspeed motor 119. The three-phase wires 114L 114L and 114L are connectedby knife switches KL KL and KL respectively, to wires 113L 113L 113L inthe motor control 113. l

For the purpose of easily following the control circuit of motor control113, the individual relays and contactors used therein are schematicallyillustrated and are dehigh speed end of a desired speed range.Conversely,

the direction switch 19 and the motor control 13 may be interconnectedso that the variable speed motor 10 will be disconnected from the powersource 11 upon the speed of the motor 10 reaching a certain minimumspeed at the low speed end of a desired speed range.

To operate the apparatus illustrated in Fig. 1 for the and the motor 19from the powersource 11. Aslong scribed with reference to theiroperating coils" and respective contacts. Each of 'the'relay contactsoperated by and associated with a particular relay coil carries that,coils reference character suflixed by a number. Further,

Energization and de-energization of the variable speed motor 110, aswell as the constant speed motor 119, is

as ,these two motors 10 and 19 are rotating at relative speeds, suchthat the variable speed motor is operating Within a'desired speed range,the differential 17 will hold the direction switch 18 in a positionpermitting motor control 13 to continue the energization of motors 10and 19. If, the speed of the variable speed motor reaches the certainspeed at one end of the desired speed range, the

differential 17 will operate switch 18 or move it to a position whereinit causes motor control 13 to discon- .operating coil M, UN, and US.

directly controlled by normally open main contacts M and M and normallyopen reversing contacts UN and UN, and U8 and U8 The main contacts M andM these contacts are normally open contacts of suitable contactors andare closable by energizing their respective It is understood that staticswitching means may be used in place of the therein described contactorsif desired to effect energization and de-energizatiou of the motors.

. The coils M, UN, andUS are energized by a circuit including. line 130,connected to phase wire 114L and a line 131, connected to phase wire114L,. These lines 130 and 131 are provided, respectively, with suitableknife switch and fuse devices 132 and 133. Connected in series with theline 130 are normally open relay contacts B and normally open relaycontacts UV each adapted to be closed upon energization of itsrespective relay coil B and UV. As is illustrated in the drawings, thereis connected in series connection between lines 130 and 131 a normallyclosed emergency stop button 134, relay contacts STR, and relay coil UV.Connected in parallel with the relay contacts 5TR are relay contacts5SCR relay contacts SNCR and series contacts UN; and U8 Connected inparallel with the relay coil UV is the relay coil B. Relay contacts SSCRsNCR and a relay coil STR, are connected in series circuit between lines130 and 131 and on the load side of contacts B and UV; so that relay STRcan be energized only when contacts B and UV; are closed.

Also connected between the lines 130 and 131 and in series circuit arenormally open relay contacts 1SCR and the contactor coil M. Shunting thecontacts 1SCR are normally open relay contacts INCR Also interconnectedbetween the lines 130 and 131 are normally open relay contacts UNCRnormally closed relay contacts'USR and the contactor coil UN, all ofwhich are connected in series. Shunting the coil UN is a relay coil UNR.

Also connected between the lines 130 and 131 are normally open relaycontacts ISCR normally closed relay contacts UNR and the contactor coilUS, all of which are connected in series. Shunting the contactor coil USis a relay coil USR. Also connected between the lines 130 and 131 arenormally open relay contacts 6NCR, and a relay coil INCR connected inseries therewith. Similarly, normally open relay contacts 6SCR areconnected in series with a relay coil ISCR and the series is thenconnected between the lines 130 and 131.

In this instance the power supply for the mine hoist is on a much lowervoltage, such, for example, 110 volts. To obtain voltage reduction thereare provided leads 230 and 231 electrically connected and energizedthrough a transformer T to and by the control lines 130 and 131. It'isunderstood that if desired the entire control circuit could be operativeat a single voltage in which case the leads 230 and 231 would becomeintegral with their respective leads 130 and 131.

Continuing the description of the control circuit there is connected inseries between the leads 230 and 231 normally open start button contactsNB, normally closed relay contacts 1SCR and a relay coil 6NCR. Shuntingthe start button contacts NB are normally open contacts UNR, and 1NCRwhich are connected in series. The

circuit further includes normally open start button contacts SB,normally closed relay contacts 1NCR and a relay coil 6SCR electricallyconnected in series between the lines 230 and 231. Shunting thepushbutton contacts SB are normally open contacts USR, and 1SCR whichare connected in series.

Directional switch As illustrated in the drawings, the directionalswitch 118 effectively has two contacts DZS and DZS,, both of which arenormally open with the contacts selectively closable dependent on thedirection of rotation of the switch. These contacts are included in thecontrol circuit 113. As illustrated the set of contacts D28 is connectedin series with a normally closed set of contacts USR and a relay coilSNCR, the series being connected between the leads 230 and 231.Similarly, the sets of contacts D28; is connected in series withnormally closed contacts relatively high voltage, such, for example, 440volts, and y it is desired to have part of the control circuit operative6 UNR; and a relay coil SSCR across the leads 230 and 231.

Difierential The differential used herein is of the well knownautomotive type which has input shafts 120 and 121 and an output shaft122. In such a differential the speed of rotation and direction ofrotation of the output shaft 122 is dependent on the relative speeds ofrotation of the input shafts 120 and 121. In this instance, the inputshaft 120 is connected by suitable mechanical connection represented bythe dash-dot line 123 to the mechanical connection 116 of the variablespeed motor 110. Similarly, the input shaft 121 is mechanicallyconnected, as represented by the dash-dot line 124, to the constantspeed motor 119. It is understood that the mechanical driving connectionrepresented by the dash-dot lines 123 and 124 may be a direct drivewherein the input shafts 120 and 121 rotate at the same speed as thespeeds of the respective motors and 119 or that the driving connectionsmay include speed changing devices such, for example, speed changingdevice 123', in connection 123, so that the input shafts and 121 rotateat a predetermined ratio to the speeds of their respective motors.

Best results have been obtained when the gear type differential operatesin a manner wherein the output shaft 122 rotates in one direction whenthe input shaft 120 is rotating slower than the input shaft 121, outputshaft 122 stands still when the input shafts 120 and 121 are rotating atthe same speed, and output shaft 122 rotates in the opposite directionwhen input shaft 120 rotates faster than the input shaft 121. Thisfeature is used to carry out the present invention by mechanicallyconnecting direction switch 118 to the output shaft 122 by a suitablemechanical connection, represented by the dash-dot line 125 andconnecting the direction switch as herein described in the motor control113. The mechanical connection 125 may include a speed changer 125', ifdesired, to magnify the movement of the output shaft 122. The directionswitch 118 is of standard construction such that operation of shaft 122holds the switch 118 in one position and non-rotation of, or rotation ofthe shaft 122 in the opposite direction moves the switch to anotherposition or to its opposite position.

The apparatus for carrying out the present invention is completed byelectrically connecting the constant speed motor to wires 115L 115L and1151.

Operation The system illustrated in Fig. 2 operates as follows: Assumeas a starting point the skip N is lower in a mine shaft than the skip Sand is to be raised, with the skip S being lowered simultaneouslytherewith. The first step in operation is to close the knife switches132 and 133 to energize the control circuit and to close the main knifeswitches KL KL; and KL;,. Closing knife switches 132 and 133 energizeslines and 131 to pass current through emergency stop button 134,contacts UN U8 coil B and coil UV. Contacts B and UV; in line 130 areclosed upon energization of the coils B and UV, thereby causingenergization of coil STR, which, in turn, closes the set of contactsSTR,. The entire control 113 is now ready for operation.

Next, the start button NB is pushed to closed position, thereby allowingcurrent to flow between lines 230 and 231 and through the buttoncontacts NB, contacts ISCR: and coil 6NCR. Energization of coil 6NCRcloses contacts 6NCR, resulting in energization of coil lNCR by thelines 130 and 131. Energization of the coil lNCR closes the sets ofcontacts 1NCR INCR 1NCR and opens the set of contacts INCR, to preventthe motor control responding to an accidental closing of the startbutton contacts SB. Closure of the sets of contacts 1NCR and INCR,energizes the coils M and UN to close the inain contactors M M and thecontactors UN UN, to

7 energize the variable speed motors 110'an'd the constant speed motor119 in the correct direction for hoisting the skip N. The constant speedmotor 119 will accelerate faster than the variable speed motors 110vbecause it is smaller and does not have to accelerate under as large aload. Thus immediately from the initial energization of the motors 110and 119, the motor 110 is rotating the difierential input 121 at a speedfaster than motor 110 is rotating the differential input 120, therebycausing the differential to move the switch 118 to the position whichpermits continued energization of the variable speed motors 110. It isnoted that the coil UNR is also energized upon closing of contacts 1NC Rto open contacts UNR and UNR and close the contacts UNR Closure ofcontacts UNR along with the prior closure of the contacts 1NCRinterlocks and thus shunts the start button contacts NB. -As long as themotors 110 and 119 arerotating with the motor 110 operating in itsnormal speed range and below its maximum safe speed, the directionalswitch 118 is positioned with its contacts DZS closed, therebyenergizing the relay coil SNCR. This results inthe closure of contacts5NCR which shunt the contacts 5TR and in the opening of contacts SNCRwhich deenergize coil SIR. After a period of time the contacts 5TR opensince they, along with the, coil STR are a part of a time-out relay.Following the opening of the contacts 5TR the coils B and UV arecontinued to be energized so long as the emergency pushbutton 134 isclosed and so long as the contacts SNCR remain closed. If, for anyreason, the speed of the motors 110 increases or starts to leave thepredetermined speed range, or if the motors 110 reach their maximum safespeed, due to the effect of the weight of the skips attempting tooverhaul the motors, the differential 117 willcause the switch 118 toopen the contacts DZS Opening the contacts DZS de-energizes coil SNCR,thus opening the contacts SNCR and de-energizing the coils B and UV.Contacts B and UV, open upon de-energization of the coils B and UV toeffectively kill the circuit by tie-energizing coils M, UN, UNR, INCRand STR thereby disconnecting the motors 110 and 119 from the source ofpower by opening the respective contacts M M UN and UN Since INCR hasbeen de-energized, contacts lNCR open to de-energize the coil 6NCR andthe entire motor control is returned to its starting position.

It is noted that unless the knife switches 132 and 133 are now opened,and since contacts UN and U5 are automatically reclosed, the coils B andUV again become energized to close their contacts B and UV;, to readythe circuit for another operation. It is further noted that continuedoperation of the motors may be stopped at any time by pressing one ofthe stop buttons 134 to deenergize the coils'B and UV. This causesdisconnection of the motors'110 and 119 in the same manner as describedwhen coils B and UV are de-energized by the switch 118.

The motor 110 and the motor 119 may be operated in the oppositedirection or reverse" direction to raise the skip S and simultaneouslylower the skip N by depressing the start pushbutton SB to efiect the"closure 'of'thecontacts M Mg and the contacts U5 andUS for energizingthe motors. The operation of the motor control circuit is very similarto that previously described but, in this instance, so long as the motor110 is operating within its correct speed range the contacts DZS areclosed thus energizing the coil SSCR. If the motors 110 start tooverspeed the switch contacts DZS are opened and the motors arecompletely disconnected'frorn the power lines.

Complete operation of the circuit when the start button SE is depressedand closed is not being described in detail since the relays thereforoperate in the same manner as those described in connection withdepressing start button NB.

The herein described control thus permits operation of the hoist so longas the motors are operated within their safe speed range and continuesenergization of the motors until they have exactly or substantiallyexactly reached their maximum safe speed. However, if the motors startto operate beyond the maximum safe speed, they will immediately bedisconnected.

I claim: I

A hoist and control therefor comprising a hoist motor responsive inspeedto the weight of a load being moved thereby in such manner that thehoist motor will operate in a safe speed range to move a load of oneweight and will be overhauled to rotate at an unsafe speed uponattempted movement of a load of another weight, a constant speed secondmotor permanently connected electrically in parallel with said hoistmotor, a control device for controlling the electrical connection anddisconnection of said parallel connected hoist and second motors to' asource of powensaid device including a differential having input shaftsadapted to be rotated at the same speed and at difierent speeds,respectively, an output shaft rotatable in accordance with thedifferential in speeds of rotation of the input shafts, means fordrivingly connecting one of said input shafts to said hoist motor forrotationin accordance with the speed of the hoist motor, said secondmotor being operable at constant speed and being drivingly connected tothe other of said input shafts to rotate said other of said input shaftscontinuously at a constant speed, contactor means operative toselectively connect and disconnect said parallel connected hoist andsecond motors to and-from said source of power, switchmeans operated bysaid output shaft and connected with said contactor means to effectoperation of said contactor means in response to the differential inspeeds of the input shafts to effect disconnection of said parallelconnected hoist and second motors when said hoist motor starts to rotateat an unsafe speed upon attempted movement of a load of said anotherweight.

References Cited in the file of this patent 1 UNITED STATES PATENTS1,048,999 Pratt been, 1912 1,672,670 Wilfart June 5, 1928 1,706,443Dekle Mar. 26, 1929 2,171,996 Schultz Sept. 5, 1939

